Gl a c ia l L ake Grindelwald
Process
Hazardous situation
Remains of the «Schlossplatte» rock-fall at the closure
of the lower end of the glacial lake
At regular intervals since 2005 a lake with no overground drainage has formed on the Lower Grindelwald Glacier. The water therefore makes its own
way through the glacial ice leading to the very
abrupt emptying of the lake. As the lake continues
to grow from one year to the next, there is an
ever increasing danger of flooding. For this reason,
in 2009 an artificial drainage gallery is being built
which will allow the water level of the lake to
be kept low and hence avert the danger of flooding.
The building of the gallery necessitates several
explosions daily.
We thank you for your understanding!
The formation of the lake
The formation of the glacial lake is a result of global
warming in the Alps. Higher temperatures over the
last few decades have caused the Lower Grindelwald
Glacier to recede dramatically. This process has been
accelerated since 2000. Today the surface of the
glacier in the area around the lake lies approximately
200 metres lower than in the years around 1860.
Without the supporting pressure of the glacier, the
sides of the mountain become unstable resulting in
landslides and falling rock.
Falling rock has covered the end of the glacier with
debris. The glacial ice below is hence protected from
the sun and melting. Higher up, the glacier continues
to recede leaving a reservoir that has no means of
over-ground drainage. A glacial lake was formed here
in 2005 for the first time. When the snow melts in
spring the meltwater collects in this reservoir. It then
finds its own way through the glacial ice to the glacier’s
underground drainage canal which lies between the
ice and the rock beneath and drains the entire glacier
into the Glacier Gorge and the Lütschine River.
Development of the volume of the lake
from 2005 to 2009 and prognosis for 2013
Schematic longitudinal section
of the reservoir and the closure
with debris at the lower end
Diagram: Geotest AG
The Corporation of Riverbed Constructions and Grindelwald Community
Chief Engineer District 1 Highway Departement Berne
The future
The volume of the lake is increasing dramatically
from year to year because the basin left by the
receding glacier is rapidly growing. Between 2014
and 2020, should the Lower Grindelwald Glacier
continue to melt at the same rate, the volume of
the lake could rise to 9 million m3.
2007
Diagram: VAW ETH Zurich
2009
2013
Hazardous situation
Mesures
Information
For further information please visit the
information stand at the car park of the
Gletscherschlucht restaurant at the Glacier
Gorge in Grindelwald and the website
www.gletschersee.ch
Drainage funnel of the lake after
the outburst of 30 May 2008
The problem
During the summer months the glacial lake can
break out spontaneously at any time as soon
as the water has found a way of draining through
the frozen bed of the lake. The greater the volume
of the water, the higher the level of the Lütschine
River rises. In future these sudden outbursts
are expected to cause extensive flooding causing
severe damage extending as far as the Interlaken
area.
The lake is under permanent surveillance. Should
there be signs of an outburst, alarm will be raised
and emergency procedures will be taken for the
protection of the population. Furthermore, reliable
protective constructions are also necessary to
prevent extensive damage. Since summer 2008
numerous measures have been tested. The most
effective remaining solution is the building of a
drainage gallery.
The diagonal gallery
You can imagine the glacial lake being like a bath
without a plughole. The aim of the diagonal gallery is
to create an artificial plughole for the bath as close
to the bottom of the lake as possible. The water level
can no longer rise beyond this point and reach such
a great volume. A spontaneous outburst would hardly
be able to cause any damage.
the water level reach the upper entrance of the gallery,
the water is lead through the gallery over a distance
of 700 metres before plummeting over a waterfall into
the Glacier Gorge. The lower 1.3 km of the gallery are
merely for reasons of access.
Longitudinal profile of the gallery
The consequences
The gallery is being built by blasting. The building
time is limited to 10 months to ensure the artificial
drain is in operation by spring 2010. During the
initial weeks, therefore, work will be carried out in
two shifts in at the area around the gallery portal,
thereafter the site will operate around the clock.
Unfortunately the building work, particularly the
blasting, will cause noise.
We kindly ask you for your understanding!
The effect of the gallery:
on the left the lake without gallery: on the right
the lake with gallery
Created by
Publisher:
Corporation of Riverbed constructions and
Grindelwald Community
The project
The gallery begins at the entrance to the Glacier Gorge
and ascends over a distance of 2 km in the flank of
the Mättenberg mountain to the glacial lake. Should
Diagram: Mätzener & Wyss AG
The responsible authority is Grindelwald Community’s
Corporation of Riverbed Constructions. The cost of
the project is around CHF 15 million and is subsidised
by the Confederation and the Canton of Berne.
Diagram: Geotest AG
Concept, text & Photos:
Nils Hählen, Chief Engineer District 1
Editor:
Suzanne Michel, Berne
Design:
Claudia Bernet, Berne
Diagrams:
Geotest AG, Mätzener & Wyss AG, Chief Engineer
of District 1, VAW ETH Zurich
Translation:
Jane Dubach, Susten VS
Printed by:
Sutter Druck AG, Grindelwald
Number of copies:
500, January 2009